Modular liquid skin heat exchanger

ABSTRACT

A liquid coolant heat exchange system for use in semimonocoque aircraft includes an arcuate planar heat sink fixed along a radius of curvature R, by forming members, a flexible arcuate planar spreader plate having a radius R 2 , such that R 1  &gt;R 2 , a heat exchange tube for transferring heat from the liquid coolant to the heat sink and means for attaching the spreader plate to the forming members to hold the spreader plate in contact with the heat sink.

BACKGROUND OF THE INVENTION

"Semimonocoque" as used herein refers to aircraft having a fuselage ofthe type constructed, at least in part, by attaching a veneer aroundforming members, such as longitudinal stringers and circumferential beltframe members, to produce a structure in which the veneer carries atleast a portion of the stresses arising in the fuselage. Many modernaircraft employ a semimonocoque design, including aircraft that areequipped with on board electronic systems and aircraft that areretrofitted with new electronic systems as such systems becomeavailable.

The present invention relates to heat transfer systems that providecooling and heat dissipation functions in semimonocoque aircraft. In oneapplication, the present invention is used to cool electronic systems onsuch aircraft. Many modern electronic systems used in aircraft generatesufficient heat to destroy or interfere with the function of individualelectronic components such as resistors, capacitors, transistors andintegrated circuits. Consequently, heat generated by these electronicsystems must be dissipated at a sufficient rate to maintain the systemtemperature at or below a predetermined upper operating limit, typicallyabout 55° C. (131° F.) for many electronic systems. Additionally, newelectronic systems must be tested prior to deployment, requiring thesystems to be temporarily installed on existing aircraft. The heat loadgenerated during testing of temporarily installed electronic systemsoften requires additional cooling capacity, above and beyond the designcapacity of the original equipment.

Conventional air conditioning equipment is one means of cooling aircraftelectronic systems. Conventional air conditioning equipment is, however,heavy, expensive, and maintenance intensive. Additionally, conventionalair conditioning systems require substantial power which, in the case ofan aircraft, must be obtained from the aircraft's engine(s) therebyreducing the aircraft's performance and increasing its fuel consumption.Heat transfer to the ambient atmosphere is a more efficient andconsiderably less expensive cooling method than conventionalrefrigeration methods for on board electronic systems. As a result, anumber of different types of heat exchanger systems which transfer heatthrough an aircraft's fuselage skin have been developed.

One such alternative system uses air as a heat transfer medium and theaircraft's fuselage skin as a heat sink. Pressurized air is circulatedpast the aircraft's fuselage skin to dissipate heat and thenrecirculated to cool on board electronic system components. Such systemsare known as air to air skin heat exchange systems. Air to air skin heatexchange systems, however, have several drawbacks.

Air has a low specific heat per unit volume, consequently, largetemperature changes are required in air to air heat exchange systems tomaintain low air flow rates. The temperature of the air entering theskin heat exchanger typically approaches the upper operating limit ofthe on board electronics, for example about 55° C. (131° F.).Preferably, the temperature of the air leaving the skin heat exchangeris as low as possible to maintain the air flow rates of the system aslow as possible. Lowering the temperature of the air leaving the air toair skin heat exchanger has the inevitable consequence of decreasing thetemperature differential across the fuselage skin, thus limiting theoperational envelope of the system to high altitudes where frigidambient temperatures exist. The volume of air recirculated in air to airskin heat exchange systems coupled with the low specific heat per volumeof air also requires large flow passages in order to maintain a workablepressure drop through the system. These large flow passages aredifficult to design and install around cramped electronics platformswhere space is at a premium and also result in relatively heavy coolingsystems. Adaptation of air to air skin heat exchange systems to existingaircraft thus requires extensive aircraft modifications which result inhigh cost and lengthy manufacturing schedules.

Moreover, the inside heat transfer film coefficient, which is usually onthe order of 5 to 10 BTU/hr ft² o R, dictates the fuselage skin arearequired for air to air skin heat exchange since the exterior filmcoefficient is much higher, on the order of 20 to 60 BTU/hr ft² o R.Thus, air to air skin heat exchange systems are incapable of takingadvantage of the available heat transfer capacity per square foot offuselage skin area.

Other alternative systems include liquid cooling systems. The use ofliquids to transfer and dissipate heat is highly utilized because fluidstypically have a very high heat capacity per unit volume compared togasses such as air. Liquid cooling systems used in aircraft typicallydissipate heat collected in a liquid coolant to the fuel located in thewing tanks with coolant to fuel heat exchangers. The fuel in turndissipates heat to the frigid atmosphere that exists at the highoperational altitudes where many modern aircraft operate.

One major disadvantage of existing aircraft liquid cooling systems,which dissipate heat to the aircraft's fuel, is that such systemsrequire extensive aircraft modification. Consequently, such systems areexpensive to design and install, especially in the case where the systemis retrofitted to an existing aircraft. Compounding this problem is thefact that the installation cost of existing aircraft liquid coolantsystems is not proportional to the installed cooling capacity. Thus, theinstallation cost of a 60 kW system of the existing type could costnearly as much as a 120 kW system. Additionally, retrofitting a liquidcoolant system into an existing aircraft is time consuming, therebyreducing aircraft availability.

U.S. Pat. No. 4,819,720, issued to Howard, discloses a heat exchangerused to cool avionic equipment whereby a liner is used to create a gapwith the aircraft's skin forming a heat transfer envelope through whichair may be circulated.

U.S. Pat. No. 2,646,971, issued to Raskin, discloses a method forattaching a fluid transferring tube to a metal plate for transfer.

U.S. Pat. No. 4,763,727, issued to Kreuzer, et al., discloses anassembly which connects a heat conducting plate to a pipe for heattransfer.

U.S. Pat. No. 4,969,409, issued to Merensky, discloses a system forcooling food and beverages on aircraft consisting of a cold air chambernext to the skin of the aircraft.

U.S. Pat. No. 3,776,305, issued to Simmons, discloses a heat transfersystem in which air flowing over a network of plates is used to cool aliquid flowing through the plates.

U.S. Pat. No. 4,057,104, issued to Altoz, discloses an electroniccomponent pod which is mounted on the exterior of the aircraft.Components in the pod are cooled by the flow of air over the exteriorsurface of the pod.

U.S. Pat. No. 4,273,183, issued to Altoz, et al., discloses aunidirectional heat transfer assembly for use between an electronicassembly on an aircraft and the skin and/or pod on the aircraft. Thedevice includes a thermal decoupler mechanism which operates todisengage a retractable interface heat transfer surface when theaircraft skin rises to a predetermined temperature.

U.S. Pat. No. 4,786,015, issued to Niggemann, discloses heat exchangertubes that are noncircular in construction and act as a load-bearingstructure for the leading edges of an air foil or the nose cone of anaircraft.

U.S. Pat. No. 4,557,319, issued to Arnold, discloses a system of heatexchanger tubes which are noncircular and are used to cool the keels ofmarine vessels.

U.S. Pat. No. 2,856,163, issued to Bidak, et al., discloses anarrangement for maintaining a tubing assembly in heat transfer contactwith a wall.

The foregoing references, the disclosures of which are incorporated intheir entireties for all purposes, do not however provide the novelmodular heat exchange system of the present invention.

SUMMARY OF THE INVENTION

The present invention provides a modular liquid coolant heat exchangesystem for use in semimonocoque aircraft. The heat exchange systemincludes individual modules each comprising an arcuate planar heat sinkfixed along a radius of curvature R, by forming members, a flexiblearcuate planar spreader plate having a radius R₂, such that R₁ >R₂, aheat exchange tube for transferring heat from the liquid coolant to theheat sink through the spreader plate and means for attaching thespreader plate to the forming members to hold the spreader plate incontact with the heat sink. The heat exchange system of the presentinvention provides numerous advantages over existing systems includingrapid and inexpensive installation, proportionality of cost to capacity,flexibility and efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cut away view of a semimonocoque aircraft employingthe heat exchange modules of the present invention.

FIG. 2 is a side view of a heat exchange module of the presentinvention;

FIG. 3 is a cross section of a heat exchange module of the presentinvention prior to installation; and

FIG. 4 is a cross section of a heat exchange module of the presentinvention as installed.

FIG. 5 is a schematic illustration of a heat exchange system employingmultiple heat exchange modules.

DETAILED DESCRIPTION

Referring now to FIG. 1, a semimonocoque aircraft 2 employing heatexchange modules 10 of the present invention is illustrated. Modules 10are mounted between stringers 24 and beltframe members 26 which comprisethe forming members to which the exterior fuselage skin 22 is attached.

Referring now to FIGS. 2 and 3, liquid heated coolant enters heatexchange module 10 through an inlet manifold 12, passes through heatexchange tube 14, and exits the module through outlet manifold 16. Theheat exchange tube 14 is typically fabricated from aluminum, copper,steel, brass or alloys thereof and may be cylindrical in cross sectionor may have flattened sides due to heat transfer considerations.Typically, heat exchange tube 14 will be arranged in a number of tubepasses as determined by the desired level of heat transfer, availablespace and other considerations. The tube passes may be parallel in whichcase each tube pass turns 180° or alternatively the tube passes may turnless than 180° to provide a continuously downsloping path to aid indraining the heat exchange tube and to facilitate thermosyphon action.

Heat from the coolant is transferred through heat exchange tube 14 tospreader plate 20, having an arcuate or curved planar geometry, which ispreferably formed from a resilient material having high thermalconductivity such as copper, aluminum or a composite material formedfrom pitch based carbon fibers such as those available from AmocoPerformance Products, Ridgefield, Conn. under the trade designation P120and P130. The pitch based carbon fiber composite material is preferredin many applications where weight is an important consideration. Sincethe spreader plate 20 is formed from a material having a high thermalconductivity, the heat load absorbed from heat exchange tube 14 isspread over areas of the spreader plate between passes of the heatexchange tube 14. Depending on the particular application and thematerials used to fabricate the heat exchange tube 14 and spreader plate20, the tube is fastened to the spreader plate through the use ofconventional methods such as brazing, welding, clamping or with acontact or thermal cement. The spreader plate 20 is mounted againstfuselage skin 22, which forms an arcuate or curved planar heat sink,permitting heat from the spreader plate 20 to be transferred to theaircraft's fuselage skin 22 where it is dissipated to the ambientenvironment. Thus, the fuselage skin serves as a heat sink for the heatexchange system.

As illustrated, the heat exchange module 10 is mounted between stringers24 and beltframe members 26. Stringers 24 and beltframe members 26comprise the forming members to which the exterior fuselage skin 22 of atypical semimonocoque aircraft is attached. The heat exchange module 10is mounted between stringers 24 with brackets comprising spring typestringer clamps 28 and tube braces 30. Alternatively, stringer clamps 28and tube braces 30 could be combined into a one piece mounting bracket.Notably, in the embodiment of the invention illustrated in FIGS. 2 and3, the use of spring type stringer clamps 28 and tube braces 30 to mountthe heat exchange module 10 does not require drilling, cutting orwelding of the stringers or fuselage thereby facilitating installationand avoiding the creation of stress points.

Referring now only to FIG. 3, the portion of the aircraft's fuselageskin 22 to which heat exchange module 10 is attached defines an archaving a radius of curvature R₁. Alternatively, spreader plate 20 andheat exchange tube 14 are formed along an arc having a radius ofcurvature R₂ such that R₁ >R₂.

As best illustrated in FIG. 4, when the heat exchange module 10 isclamped to the aircraft fuselage with stringer clamps 28 and tube braces30, the spreader plate 20 and heat exchange tube 14 are pushed againstthe fuselage skin 22 along the arc defined by the fuselage skin creatinga reactionary spring like force that thrusts the heat exchange module 10against the fuselage skin 22 across the area of the spreader plate 20 tofacilitate heat transfer from the spreader plate 20 to the fuselageskin. Additionally, in some applications, it may also be desirable tocoat the surface of spreader plate 20 and/or the fuselage skin 22 with acontact or thermal cement prior to installation to reduce contactresistance.

In order to facilitate a uniform distribution of the heat load, thethickness of the spreader plate 20 may vary with the thermalconductivity of the fuselage skin 22, operating temperature, tubespacing and other design parameters. Liquid coolants suitable for use inconnection with the present invention include water, ethyleneglycol/water, Coolanols, Poly Alpha Olanol or cooling slurries(microencapsulated phase change materials in coolant fluids). Liquidcoolant is circulated through the heat exchange module 10 with a pump,or alteratively, thermosyphon action may be used to circulate thecoolant.

Referring now to FIG. 5, a heat exchange system utilizing multiple heatexchange modules 10 is schematically illustrated. Pump 50 circulatesheated liquid coolant through inlet manifold 12 to individual heatexchange modules 10. Inlet and outlet valves 52 and 54 allow individualmodules to be isolated from the system while bypass valves 56 allow forthe modules to be connected in series or in parallel as desired. Liquidcoolant exiting the modules is recirculated via return line 58 to coolelectronics module 60. Other piping and valving arrangements may be usedto interconnect individual modules depending upon the particularapplication and design requirements.

Thus, the heat exchange system of the present invention, because of itsmodular design, enables rapid and inexpensive installation of moderatelysized liquid cooling systems for liquid cooled on board aircraftelectronics. The modular design of the heat exchange system of thepresent invention also permits installation of an aircraft liquidcooling system consisting of multiple identical modules resulting ineconomies of high manufacturing quantities and commonality of parts.

Moreover, the modularity of the invention results in proportionalitybetween the cooling capacity of a liquid cooling system and theinstallation cost of the system permitting earlier and experimentalintroduction of liquid cooled electronics and new liquid cooling fluidssuch as microencapsulated phase change materials. Additionally, the heatexchange system of the present invention is installed with little or nostructural modification permitting rapid and easy removal of the systemsubsequent to trial deployment of liquid cooled electronics. The modulardesign of the system also permits incremental upgrading of the system asthe cooling demands increase. In the case of a failure, a single modulecan be isolated allowing the remainder of the system to operate. Thefailed module can then be scheduled for replacement at a convenient timewhereas failure of existing systems may dictate that the aircraft betaken out of service immediately for extensive repairs.

While the present invention has been described in connection with theillustrated embodiments, it is not intended to limit the invention tothe particular forms set forth, but on the contrary, it is intended tocover such alternatives, modifications, and equivalents as may beincluded in the spirit and scope of the invention as defined in thefollowing claims.

I claim:
 1. A liquid coolant heat exchange system comprising:an arcuateplanar heat sink having an inner surface; forming members for supportingsaid arcuate planar heat sink along a radius of curvature R₁ ; aflexible arcuate planar spreader plate having an outer surface and aradius R₂, such that R₁ >R₂ ; a heat exchange tube attached to saidflexible arcuate planar spreader plate in a substantially abuttingrelationship; means for attaching said arcuate planar spreader plate tosaid forming members, and for positioning the outer surface of saidarcuate planar spreader plate in substantially abutting relationshipwith the inner surface of said arcuate planar heat sink for transferringheat from said heat exchange tube to said arcuate planar heat sink. 2.The heat exchange system of claim 1 wherein said arcuate planar heatsink comprises a fuselage skin of an aircraft.
 3. The heat exchangesystem of claim 1 wherein said arcuate planar spreader plate comprises acarbon fiber composite material.
 4. A heat exchange system comprising:anarcuate planar heat sink having an inner surface with a radius ofcurvature R₁ ; and a plurality of interconnected heat exchange modulesmounted to the arcuate planar heat sink, each module comprising:aflexible arcuate planar spreader plate having an outer surface with aradius of curvature of R₂, wherein R₁ >R₂ ; a heat exchange tubepositioned in substantially abutting relationship with said flexiblearcuate planar spreader plate; and means for mounting said arcuateplanar spreader plate to said arcuate planar heat sink to position theouter surface of said arcuate planar spreader plate in substantiallyabutting relationship with the inner surface of said arcuate planar heatsink for transferring heat from said heat exchange tube to said arcuateplanar heat sink.
 5. The heat exchange system of claim 4 including meansfor connecting said modules in series to form a cooling circuit.
 6. Theheat exchange system of claim 4 wherein said modules are connected inparallel to form a cooling circuit.
 7. The heat exchange system of claim4 wherein each said arcuate planar spreader plate comprises a carbonfiber composite material.
 8. An aircraft including a heat exchangesystem comprising:an arcuate planar heat sink; forming members forsupporting said arcuate planar heat sink along a radius of curvature R₁; and at least one heat exchange module, comprising:a flexible arcuateplanar spreader plate having a radius R₂, such that R₁ >R₂ ; a heatexchange tube attached to said flexible arcuate planar spreader plate ina substantially abutting relationship; and means for mounting saidarcuate planar spreader plate to said forming members and forpositioning said arcuate planar spreader plate into surface contact withsaid arcuate planar heat sink for transferring heat from said heatexchange tube to said arcuate planar heat sink.
 9. The aircraft of claim8 wherein said arcuate planar heat sink comprises the fuselage skin ofthe aircraft.
 10. The aircraft of 8 wherein said arcuate planar spreaderplate comprises a carbon filter composite material.
 11. The aircraft ofclaim 8 further comprising a plurality of heat exchange modules.
 12. Theaircraft of claim 11 including means for connecting said modules inseries to form a cooling circuit.
 13. The aircraft of claim 11 whereinsaid modules are connected in parallel to form a cooling circuit.